Answer to Question 1
Hot spots are stationary mantle plumes that form deep within the mantle, and can produce a set of volcanic islands such as the Hawaiian island chain. Hot-spot volcanism is not related to volcanism in subduction zones.Subduction zone is a deep trench where one plate slides under another. Melting releases low-density magma that rises to form volcanoes such as those along the northwest coast of North America, including Mt. St. Helens.
Answer to Question 2
Cepheid variables
RR Lyrae variables
pulsating stars